Protective system



2 Sheets-Sheet l EEE E Nk

Nov. 9, 1937.

Nov. 9, 1937. R. R, GooDRlcH 2,098,384

PROTECTIVE SYSTEM Filed May 19, 1954 2. sheets-sheet 2 L s@ 1g b u #c wsj f l1 a wg AA AA VVVVV A I Hy .65 1 .5.0 .55 445.

Patented Nov. 9, 1937 PROTECTIVE SYSTEM B. Goodrich, Camden, N. J., assigner to Radio Corporation of America, a corporation of Delaware Application May 19, 1934, Scl'lll No. '38,442

6Clainis.

My invention relates to protective systems and more particularly to systems for protecting cathode-ray tubes against destructive beam-current.

When cathode-ray tubes are utilized in television receivers or for the purpose of alternating current analysis and the like, it is customary to provide ray-deecting devices which cause the ray, or beam to periodically traverse the fluorescent screen in a pre-determined pattern. If, by reason of failure of the ray-deflecting devices, etc., the ray comes to rest upon the uorescent screen and remains stationary for even a very short time the screen is burned and the tube is rendered substantially useless for satisfactory picture reception.

It is, accordingly, an object of my present invention to provide means whereby .failure of the ray-deflection generators associated withv a cathode-ray tube does not occasion the ow of destructive b current.

Another object of my invention is to provide a protective system lfor a cathode-ray tube that shallv function to prevent destructive beam-current in the event of breakage of certain essential circuit connections.

A still further and more specific object of my invention is to provide a protective system for a cathode-ray tube that shall function to prevent destructive beam-current in the event that certain essential connections in the protective system, itself, are broken.

In accordance with my invention, I prefer to accomplish the foregoing objects by providing means for depriving the rst anode, in a. cathode-ray tube, of positive potential in the event that the ray ceases to be deflected according to a pre-determined pattern. Specifically, I provide a relay for connecting the second anode to ground and for simultaneously de-energizing the source which supplies it with potential and I make use of a unidirectional current derived from the ray-deecting devices for. determining the operation of the relay. In addition, I so interconnect the relay and the current-deriving means that failure of the latter also causes the relay to drop out, thus aiording added protection.

The novel features that I consider characteristic of my invention are set forth with particulax'ity in the appended claims. The invention it- 5 self, however, both as to its organization and its method of operation, together with additional objects and advantages thereof, will best be understood from the following description of a. specific embodiment, when read in connection with the 55 accompanying drawings, in which:

(Cl. Z50-27) Figure 1 is a view of a portion of a television receiving system in which an embodiment of my invention is included, and

Fig. 2 is a view of a portion of a television receiver including an alternative embodiment of my invention.

In both figures, like elements are similarly designated.

Referring now to Fig. 1 of the drawings, a cathode-ray tube I of the general type to which my invention pertains is constituted by an evaculated envelope having a bulbous portion 3 and a cylindrical portion 5. 'I'he interior wall oi the bulbous portion may be provided with a. metallic coating 'l to serve as a second anode and the large end is provided with an interior fluorescent screen 9 usually made from Willemite or the like. An electron gun, constituted by an equipotential cathode Il, a grid i3 and a first anode i4, is disposed in the cylindrical portion of the tube. Suitable grid-cathode biasing potential and anode potential is provided from a common source, exemplified in the drawings by a bleeder resistor I5 connected across the output terminals of a rectiiier Il, over a plurality of conductive connections I9, 2|, 23 and allocated, respectively, to the grid, the cathode, the rst anode and the second anode.

In order that a two-dimensional picture may be reproduced on the uorescent screen, means are provided for causing the ray to simultaneously traverse the screen in two directions normal to each other. In an actual commercial system ray-deflection may be accomplished by utilizing electromagnetic deiection coils alone, electrostatic defiecting plates alone or by a combination of coils and plates.

In order to simplify the drawings I have exemplied the vertical deecting system by a singie coil 2l connected to the output terminals of a ray-deflection impulse generator 2l and the horizontal deecting system also by a single coil 3l connected to the output terminals of a raydeiiection impulse generator Il. It is to be understood, of course, that in the system as actual- 1y constructed each of the single coils is replaced by a pair of coils connected in series-aiding relation and disposed at opposite sides of the cylindrical portion of the tube.

The generators maybe of the continuous oscillation type, merely synchronized by incoming synchronizing impulses, or they may be of the intermittent type which only functions to provide output impulses when triggered-oil' by the 55 apparent hereinafter, is applicable to either type. If. during the operation of the system thus far described, for translating incoming picture-l signals into a visml reproductionof the transmitted view, the deiiecting generators should fail simultaneously the fluorescent screen in the tube would immediately be ruined. Even though but one of the generatorsV should fail. or the connections between it and the deiiecting coils should break, thesereenmightbe spoiledsincetheray. traversing the screen in a single direction under an accelerating potential of the order of 10,000 volts, causes much higher localised heating than normal.

In accordance with my invention, therefore, I provide means, responsive to de-energisation of one or both of thedeiiecting coils. for depriving the ray of accelerating potential.

Referring oncemoretoFig. Litwill benoted that the circuit for supplying the primary windlng 8l of a power transformer 31 feeding the rectiner includes an armature Il and a fixed :ontact Il of a'relay Il. It will also be noted :hat the relay is provided with a second grounded armature Il which is connected to the cathode if the cathode-ray tube and is normally held sway from a nxed contact 41 from which a coniection 49 extends to the rst anode il in the :athode-ray tube. The armatures are interconaected by an insulator Il for simultaneous movenent.

Obviously, when the relay is energized' the Lrmature is drawn up and held to complete the :nergizing circuit for the primary winding of the :ower transformer. When it drops out. the energizing circuit is broken and the iirst anode is zonnected directly to the cathode and to ground, ilus depriving it of potential.

In order that the position of the armatures nay be so controlled by the ray-denecting imiulses that they will drop out upon failure thereif, I connect the relay winding between the anode i3 of a thermionic device Il, hereinafter called .he control tube, and the positive end of a leeder resistor 55 connected across the termiials of a source I1 preferably of unidirectional iotential such as a battery or rectifier but an ilternating current source may be used. The athode of the control tube is connected to an ntermediate point on the bleeder resistor and i fixed or static negative bias suiiicient to stop he ilow of output current is provided by conlecting the grid to the negative end of the reistor.

Since, in the operation of the system. the conrol tube must conduct current to energize the `clay just so long as the ray-deliection coils are lnergized from the ray-deflection generators, I rovide further means for deriving positive poentials from the deflection impulses and for utilzing them to nullify the xed negative potential lerived from the bleeder resistor.

Speciilcally, I prefer to include a plurality of esistors 59 and 8i inthe input circuit of the ontrol tube, between the grid and cathode thereif, and cause unidirectional currents derived from he ray-deiiection impulses to ilow therein when he system is in operation.

To provide a current proportional to the horiontal impulses I connect one of the resistors 59) between the cathode and anode of a diode ectiiier 6I, including in the circuit the secondary 5 of a transformer 61 the primary I9 of which i connected in series in the horizontal ray-deneocon circuit. a similar diode 1| 1s connected across the other resistor (li) and it is fed froml the vertical ray-deiiection circuit through a similar transformer 18.

As will be clear from the drawing, theseveral diodes are so connected to the resisten that the rectified current iiowing sets up potentials in opposition to the negative potential impressed upon the grid of the control tube from the potential supply resistor Il. 'ihrough proper choice of the constants of the system the static negative potential may be overcome and the grid of the control tube given the proper positive potential to permit just enough space current to ow in the relay winding to pull up and hold the armatures. After the proper balance has been obtained, if either or both diodes are deprived of input excitation the iiow of space current in the control-tube is so reduced that the armatures dropandaswillbeclearly apparentfromthe drawings, the iirst anode in the cathode-ray tube is immediately connected to ground and the rectifler supplying potential thereto is de-energiaed.

In order to provide a further measure of safety I prefer to utilise equipotential -cathodes in the diodes and in the control tube and to energize them in parallel from a power transformer 1l the primary 'I1 oi.' which is energized in parallel with the primary winding Il of the power transformer I1 energizing the main rectier I1. The failure of either diode cathode-heater, the; efore, deprives the grid of the control-tube ofa portion of the neutralizing potential, thus de-energizing the relay. Also, should the control-tube cathodeheater fail, the same action, obviously, takes it 'expedient to connect a reasonably large capacitor II in shunt with each o! the diode-output-resistors. Each capacitor, for example, may have a capacity of .015 mfd., and each resistor may be .2 megohm. Further a reactor-condenser nlter may be interposed between the output resistors l. and .i and the input terminals of the controltube for the same purpose although such a illter is not usually necessary. Such a filter is exemplified in the drawings by a sexies connected resistor 8i and a plurality of shunt condensers Il. Naturally, an inductor may be substituted for the filter-resistor if desired.

It might be inferred from the foregoing that my invention is limited to cathode-ray tube systems wherein deflection of the ray is accomplished through the use of electromagnetic deflection coils. Such is not the case. however, since the basic principle thereof is equally as well applicable to systems wherein electrostatic forces are employed for deection or to those of the type wherein deflection in one direction is obtained electromagnetically and in the other direction electrostatically.

For example, referring now to Pig. 2 of the drawings, if ray deflection in any given direction is accomplished by impressing a saw-tooth or sinusoidal potential across a plurality of plates 85 disposed in the cylindrical portion of the cathode-ray tube I, such potentials may also be utilized to determine the working bias on the grid of the control-tube I4. For the foregoing purpose, I prefer to utilize the thermionlc tube Il' having two grids I9 and Il, an equipotential cathode 93 and either a common anode Sl, as illustrated, or two electrically connected anodes, one for each grid. A source 0l of anode and biasing potential is of course provided. Tha

`als

grids are coupled to the ray-denection plates through stopping condensers ll and il, respectively, and the device is provided with an output, or self-bias resistor IM around which a reasonably large capacitor |03 is connected.

'Ihe self-bias resistor is included in the input circuit of the control tube, the connections being such that the potential across it bucks" the static negative potential on the grid. As is well known to those skilled in the art, the average plate current from a thermionic device which obtains its bias from a self-bias resistor is substantially constant although it does increase slightly in response to the presence of grid excitation. By careful adjustment, the space current in the excited condition may be made to override the static negative potential on the grid of the control-tube and the system functions in substantially the same manner as the system exemplified by Fig. 1.

It should be apparent from the foregoing that my improved protective system has many advantages. If either of the deection generators fails, the beam is immediately cut o and this action also takes place if any of the connections between the generators and the deilecting coils or plates should break. Furthermore, should the control tube be deprived of positive biasing potential by failure of any element in the protective to notify the operator that repairs should bemade.

Although I have chosen several specific embodiments of my invention for purposes of illustration, many other obvious modifications will be apparent to those skilled in the art. My invention,ltherefor e, is not to be limited except insofar as is necessitated by the prior art and by the spirit of the appended claims.

I claim as my invention:

1. In combination, a cathode ray tube having a uorescent screen, means within the tube for developing a cathode ray and directing it toward the screen, means for deilecting the rayacross the screen according to a predetermined recurrent pattern, a ray-accelerating anode within the tube, connections for supplying a potential to the anode and means for depriving the anode of potential and connecting it to ground upon failure of the ray-deflecting means.

2. In combination, a cathode ray tube having a fluorescent screen, means within the tube for developing a cathode ray and directing it toward the screen, means for detlecting the ray across the screen according to a pre-'determined pattern,

means for deriving a unidirectional potential from the ray-deflecting means, connections for supplying anode potential to the tube and means responsive to said unidirectionall potential for determining the continuity of said connections.

3. In combination, a cathode ray tube having a fluorescent screen, means within the tube for developing a cathode ray and directing it toward the screen, means for defiecting the ray across the screen according toa pre-determined pattern,

connections for supplying anode potential to said tube, switching means included in said connections and means responsive to the energization of said ray-deileeting means for determining the operation of said switching means.

4. In combination, a cathode ray tube having a fluorescent screen, means within the tube for developing a cathode ray and directing it toward the screen, an accelerating anode interposed between the said means and the screen, means including a source of fluctuating potential for causing the ray to traverse the screen according to a pre-determined pattern, a unidirectional potential source, a thermionic tube having an output circuit including the winding of a relay, a movable armature and a fixed contact associated with the relay winding, connections whereby the armature and the contact connect the unidirectional potential source to the accelerating anode upon energization of the relay winding, means for normally biasing the thermionic tube negatively to substantially the cut-on potential, means for deriving a unidirectional potential from the source of fluctuating potential, and connections for utilizing the derived unidirectional potential to nulllfy the said normal negative bias whereby, when the ray is being deected across the screen the anode is supplied with potential and potential is removed therefrom upon failure of the fluctuating potential supplying means.

5. The invention set forth in claim 4, characterized in that the unipotential deriving means includes a thermionic tube and additionally characterized inthat connections are provided whereby cathode heating potential may be applied to.

potential, a source of unidirectional potential,

means responsive to space current in said thermionic tube for establishing a connection between the accelerating anode and the unidirectional potential source, means responsive lto absence of current in said tube for establishing a connection between the accelerating anode and the cathode, means for deriving unidirectional potentials from each fluctuating potential source and connections whereby said unidirectional potentials are utilised coniointly to nullify 'the normal negative bias applied to the thermionic tube whereby, when the ray is being deflected according to a predetermined pattern potential is applied to the accelerating anode and when deilection according to said pattern the said anode is connected to said cathode to prevent the cathode ray from causing damage to the fluorescent screen.

ROBERT R. GOODRICH. 

